A motor-driven vehicle such as an electric vehicle (EV) or a plug-in hybrid vehicle (PHV) uses an electric motor as a drive power source for vehicle travel. In the vehicle, it is necessary to charge a battery, which supplies the motor with electric power, when the amount of electric power remaining in the battery (stored electric charge of the battery) falls. It is therefore proposed to assist a driver of the vehicle so that the battery may be charged before the battery runs down and the vehicle becomes inoperative.
For example, the following patent document 1 discloses a technology, which calculates a travelable distance (further travel distance) when a remaining electric power amount of a battery falls below a predetermined level. The technology further provides a driver with position information about an electric energy supply station (charging station) located near a present position of the vehicle as well as discrimination information about possibility of arriving at the charging station. The travelable distance of the vehicle is calculated based on the remaining electric power amount of the battery.
Further, the following patent document 2 discloses another technology, which selects a charging station located near a present position of a vehicle out of a plurality of pre-stored charging stations and provides a driver of the vehicle the location of the selected charging station as well as availability of an electric battery charger installed in the selected charging station. Patent document 2 further discloses a technology, which checks at a predetermined time interval whether it is possible to continue to travel to the destination without charging the battery. This checking may be made based on the remaining electric power amount of the battery of the vehicle and an amount of electric power required for the vehicle to travel from the present position to the destination. According to this technology, if it is determined that it is not possible to reach the destination with only the remaining electric power of the battery, the charging of the battery can be started immediately or within a predetermined time after arriving at the charging station and information about the charger device, which can charge the battery to the required capacity.
Patent document 1: JP 9-210702A
Patent document 2: JP 2003-262525A
For traveling from a departure point to a destination point without being constrained too much in time, it is essential to plan a travel schedule, which determines the time of departure based on the scheduled time of arrival at the destination point so that the driver need not be so hasty in driving the vehicle. It is also essential that the driver need not worry about so much whether the user can reach the destination point with the remaining electric power amount of the battery, which varies from time to time.
In this regard, the technology of patent document 1 provides only information about charging stations, which are located near the vehicle when the remaining electric power amount falls below the predetermined level. It is not clear whether the vehicle can reach the destination with only the remaining electric power amount of the battery available at present. Thus, the technology of patent document 1 cannot provide the driver with sufficient reassurance. The technology of patent document 1 does not provide the driver with information whether the driver can reach the destination with only the presently available remaining capacity. The driver thus cannot take into consideration the necessity of charging the battery or the charging time of the battery, and hence cannot plan the travel schedule with sufficient time allowance.
According to the technology of patent document 2, although it is possible to check whether the vehicle can reach the destination with only the remaining electric power amount of the battery, it is not possible to plan a travel schedule at the time of departure of the vehicle in consideration of the remaining electric power amount of the battery. The driver thus cannot plan the travel schedule with sufficient time allowance, according to the technology of patent document 2.